Lecture 20

• Arose 2.0 - 1.9 BYA
• Eukaryotes came after:
• - the rise of atmospheric oxygen
• - the invention of respiratory metabolism in Bacteria
• - the development of enzymes such as superoxide dimutase, which detoxifies oxygen radicals generated as a by-product of aerobic repsiration
• Oldest known microfossil is ~2billion years old
• Fossils of increasing complexity are evdident from 1.9 to 1.4 BYA

• Contain a membrande-enclosed nucleus, mitochondria, chloroplats (phototrophs), Golgi complex, peroxisomes, lysosomes, endoplasmic reticula, micotubules, and microfilaments
• Includes: protists, fungi, unicellular red algae, and unicellular green algae

• Repsiratory organelle of aerobic Eukarya
• site of respiratory enzymes and oxidative phosphorlyation
• Cristae- internal membranes, sites of enzymes for respiration and ATP synthesis
• Matrix- enzymes for oxidation of organic compounds
• Evolutionary origin- falcutatively aerobic Alphaproteobacterium ~2BYA

• Organelle of photosynthesis in phototrophic Eukarya
• Stroma- lumen of chloroplast, site of enzymes of the Calvin cycle
• Thylakoids- flattened membrane discs, site of chlorophyll and other components involved in capturing light engergy
• Evolutionary origin- a cyanobacterium ~1.5BYA

• 1. Mitochondria and chloroplasts have DNA for rRNAs, tRNAs, and respiration/photosynthesis
• 2. Eukaryotic nucleus contains bacterial genes derived from mt and chl
• 3. Mt and chl have their own ribosomes with 70S size like in Bacteria
• 4. Antibiotics that kill or inhibit Bacterial 70S ribosome function also interfere with protein synthesis in mt and chl
• 5. Phlyogenetic analysis based on 16S rRNA gene sequencing places mt and chl in domain Bacteria

• Certain Eukarya thought to lack mitochondria have been found to have hydrogensomes
• Found in obligate or aerotolerant anaerobes (in anaerobic Eukarya)
• Lack enzymes of the citric acid cycle, usually lack cristae, and oxidizes pyruvate to acetate, H₂ and CO₂
• Allows ATP to be made by SLP
• Contain DNA and ribosomes and functions as a fermentive organelle
• Metabolically degenerate mitochondria

• Relic mitochondria
• Found in some eukaryotes that lack mitochondria and hydrogensomes
• Clustered mitochondria-like proteins surrounded by tiny double membrane sacs
• Derived from mitochondria, but even more degenerate than hydrogensomes

• 1. Aquisition of the mitochondrian led to the origin and massive evolutionary radiation of Eukarya
• 2. Later aquistion of the chloroplast by one of the Eukarya lineages resulted in phototrophic eukaryotes

A nucleus bearing cell spontaneously arose from an early kind of cell before the divergence of Bacteria and Archaea in response to teh increasing genome size of the early eukaryote

A hydrogen-dependent host aquired a facultatively aerobic symbiont

• SSU rRNA gene sequence is mor similar to Archaea than Bacteria
• Transcription/translation apparatus has many similarities to Archaea
• Lipids are ester-linked like Bacteria
• Energy metabolism is mor similar to Bacteria